Hydronic heating
Hydronic heating circulates heated water through radiators or in-slab loops. How it's installed, why in-slab is a slab-stage job, and its NCC energy impact.
Ask Chalkline about this →A hydronic heating system warms a building by circulating heated water through a sealed loop of pipework to panel radiators, towel rails, or in-slab coils cast into a concrete floor. A central heat source (a gas boiler or, increasingly, an electric heat pump) raises the water temperature, a circulating pump pushes it around the loop, and valves or zone thermostats control each area. Because the heat is carried in water rather than blown as air, the warmth is even and quiet, with no draughts or fan noise.
Where it sits in the build
- In-slab loops are laid and pressure-tested before the pour, then cast into the concrete, so the slab itself becomes the radiator. This is a slab-stage job, not a first fix one, and it cannot be retrofitted once the slab is down.
- Panel radiator systems are roughed in at first fix plumbing: flow and return pipes are run in walls and floors and capped off, then the radiators are hung at second fix.
- The heat source and pump are commissioned near handover, alongside other HVAC plant.
A plumber installs and pressure-tests the wet side; a sparky wires the heat-source controls and pump.
Why it matters
The heat source drives both running cost and compliance. A heat-pump (reverse-cycle) source is efficient and generally scores well in the NCC Whole of Home energy budget; a gas-fired boiler ties the system to a gas supply and generally scores worse on the same budget. In-slab systems are slow to respond (the slab takes hours to warm up and cool down), so they suit steady background heat rather than quick on-off use.
Also known as: hydronics, wet underfloor heating (in-slab), radiator heating.
Category: Mechanical services / heating
Related
- HVAC, the broader category of installed heating, ventilation and cooling plant
- First fix and second fix sequence, where the pipe rough-in lands in the build
- Timber floor coverings, what can sit over a heated slab
See also
- Whole of Home, the NCC energy budget the heat source feeds into
- Screed, the topping that can encase floor loops
- Plumber, the trade that installs and pressure-tests the wet side
Last updated: 2026-05-26. Verified: 2026-05-26. Quarterly review for currency.